The present invention relates to a high-frequency ring resonator for use in a radio communication apparatus and a ring antenna.
A radio communication apparatus is advantageous in that it can be easily configured as a communication apparatus excellent in portability, as compared to a wire communication apparatus. This apparatus in many cases requires size-reduction in order to enhance carryability. Consequently, size reduction is required also for the elements constituting the apparatus.
The small resonator, for use in high-frequency filters, oscillators or the like, often utilizes a TEM-mode one-wavelength ring resonator as shown in FIG. 1.
The upper conductor 101 and the lower conductor 102 are structured on the opposite surfaces of a dielectric substrate 100, thereby constituting a one-wavelength ring resonator. An input signal is applied through a coupling capacitor 103 to point a on the upper conductor 101. A resonant signal is outputted from point b where the electrical length corresponds to the half wavelength at the resonant frequency, and passes through the coupling capacitor 104, thus configuring a high-Q resonator.
The resonator, because an upper conductor 101, coupling capacitors 103, 104, etc. can be formed on a dielectric substrate 100 by a print or photo-etching technique, is well suited for mass production and has good reproducibility of desired characteristics.
In order to reduce the size of the one-wavelength resonator, there is a proposal that a gap is provided in the upper conductor 101 as a resonant line, a capacitance is connected in the gap, and a transmission line is coupled to the resonator, thereby extracting an output. This configuration can decrease the resonant-circuit resonant line length down to one wavelength or smaller, hence allowing for making a miniature resonator structure. However, the Q-value of the resonator might decrease due to lumped constant elements in the resonant circuit. Thus, this resonator tends to suffer deterioration in Q-value, more so than the one-wavelength ring resonator.
Meanwhile, a ring antenna is well known as an antenna for use in an RF apparatus. FIG. 2 shows a conventional structure of a ring antenna. The conductor 1101, being a balanced circuit having an electrical length corresponding to one wavelength at the resonant frequency, is connected at its end with a balun 1102. Output is generated from the unbalanced circuit of the balun 1102.
The ring antenna, simple in structure, is well suited for mass production and has good reproducibility of desired characteristics.
However, the ring antenna, on the principle, requires a line length corresponding to one wavelength. This increases the size particularly in a frequency band having a long wavelength, resulting in difficulty in manufacturing a portable radio frequency apparatus.
It is a first object of the resent invention to reduce the size of the resonator without encountering deterioration in Q-value.
A second object is to reduce the size of the ring antenna structure.
According to the present invention, when the transmission line in a TEM mode is structured by two conductors, the ends of these line are connected with opposite polarity to the ends of the other line, thereby constituting a resonator resonating in a half-wavelength mode. This structure, free of line discontinuity to deteriorate the Q value, can constitute a resonator having a high Q-value equivalent to that of the one-wavelength resonator. Moreover, the transmission line length is satisfactorily a half of that of the one-wavelength resonator. Accordingly, it is possible to miniaturize the form with a structure that has little Q-value deterioration.
Meanwhile, because there is no line discontinuity deteriorating characteristics, an antenna can be structured high in efficiency equivalent to the one-wavelength ring antenna. Accordingly, it is possible to reduce the size down to half that of the conventional antenna.
Furthermore, size reduction is further possible by inserting a capacitance element in the ring antenna circuit.